Method of fabricating microelectromechanical systems devices

ABSTRACT

A method of fabricating microelectromechanical systems devices is disclosed. A silicon substrate having a plurality of microelectromechanical systems elements formed on a first surface thereof is provided. A guard layer defining a plurality of recesses is applied to the silicon substrate such that respective microelectromechanical systems elements are located within respective recesses. The silicon substrate is then segmented into discrete parts and an adhesive layer is bonded to a second surface of the silicon substrate. The guard layer is next segmented into discrete parts corresponding to the discrete parts of the silicon substrate, thereby forming individual microelectromechanical systems devices. Finally, the adhesive layer is selectively exposed to a light source allowing removal of individual microelectromechanical systems devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application a continuation application of U.S. application Ser. No. 12/268,966 filed on Nov. 11, 2008, which is a continuation application of U.S. application Ser. No. 11/450,431 filed on Jun. 12, 2006, now issued U.S. Pat. No. 7,465,405, which is a continuation application of U.S. application Ser. No. 10/296,660 filed on Aug. 1, 2003, now issued U.S. Pat. No. 7,063,993, which is a national phase (371) application of PCT/AU00/00583, filed on May 24, 2000, all of which are herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the fabrication of devices incorporating microelectromechanical systems (MEMS). More particularly, the invention relates to a method of fabricating a MEMS device using at least one UV curable tape. For the sake of brevity, such a device shall be referred to below as a MEMS device and the part of the device comprising the microelectromechanical system shall be referred to as a MEMS layer.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a method of fabricating microelectromechanical systems devices, the method comprising the steps of:

-   -   forming a plurality of microelectromechanical systems elements         on a first surface of a silicon substrate;     -   applying a guard layer to the first surface of the silicon         substrate, the guard layer defining a plurality of recesses and         respective microelectromechanical systems elements are received         within respective recesses;     -   segmenting the silicon substrate into discrete parts, each         discrete part including at least one microelectromechanical         systems element;     -   bonding an adhesive layer to a second surface of the silicon         substrate, the second surface being opposite said first surface;     -   segmenting the guard layer corresponding to the discrete parts         of the silicon substrate thereby forming individual         microelectromechanical systems devices; and     -   selectively exposing the adhesive layer to a light source         allowing removal of individual microelectromechanical systems         devices.

Various other aspects of the present invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example with reference to the accompanying diagrammatic drawings in which:

FIGS. 1 to 8 show various stages in a method of fabricating MEMS devices, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

In an initial step, illustrated at 10 in FIG. 1 of the drawings, of a method of fabricating a MEMS device, in accordance with the invention, a layer 10 is provided to be applied to a first surface 12 of a silicon substrate or wafer 14. The wafer 14 carries a surface macromachined MEMS layer 16 on the first surface 12 of the wafer 14. The MEMS layer 16 comprises individual MEMS elements 18.

The invention has particular application in the manufacture of ink jet printheads. For ease of explanation, the invention will be described with reference to that application. Thus, the layer 10 is a nozzle guard layer or wafer which is applied to the surface 12 of the silicon substrate 14. Each individual MEMS element 18 is in the form of a nozzle assembly. Each nozzle assembly 18 comprises an ink ejection nozzle and its associated actuator. The actuator acts on the nozzle for effecting ink ejection, on demand.

The purpose of the method of manufacture is to form individual MEMS chips 20 (FIG. 8).

Hence, after the nozzle guard layer 10 has been applied to the wafer 14, the wafer 14 is turned over to expose a reverse side 22 as shown in FIG. 3 of the drawings.

Various operations are then carried out on the wafer 14. In particular, the wafer 14 is back etched, from the surface 22 towards the surface 12 to separate the silicon wafer into discrete parts 24. In addition, in this application of the invention, ink inlet apertures 26 are etched through the parts 24. It is to be noted that each part 24 comprises a plurality of MEMS elements 18 and a bond pad 28. Also, as shown more clearly in FIG. 1 of the drawings, the layer 10 has a plurality of struts 30 which support a body 32 of the layer 10 in spaced relationship above the surface 12 of the wafer 14 such that the MEMS elements 18 and the bond pads 28 are protected by the body 32. The struts 30 define chambers 34 and 36. The chambers 34 overlie the bond pads 28 while the chambers 36 overlie the array of MEMS elements 18 of each part 24.

A holding means in the form of an adhesive tape 38 is bonded to the surface 22 of the layer 14 as illustrated in FIG. 5 of the drawings. The tape 38 is bonded to the layer 14 by means of a curable adhesive. The adhesive is curable in the sense that it loses its adhesive properties or “tackiness” when exposed to ultraviolet (UV) light.

Depending on the equipment used, a handling means in the form of a glass, quartz, alumina or other transparent handle wafer 40 is secured to an opposite surface of the tape 38.

The wafer 40, the tape 38, the silicon wafer 14 and the nozzle guard layer 10 define a laminate 42. The laminate 42 is then turned over, as shown in FIG. 7 of the drawings.

Predetermined operations are carried out on the layer 10. More particularly, passages 44 are etched through the layer 10 from an outer surface 46 towards the chambers 36. In addition, individual nozzle guards 48 are formed by etching to remove material as shown at 50 in FIG. 7 of the drawings. The removal of this material exposes the bond pads 28 of each chip 20. Upon completion of this operation, the individual chips 20 are formed.

In this embodiment of the invention, each chip 20 has a plurality of MEMS elements 18 in an array formed thereon.

The laminate 42 is placed on an xy wafer stage (not shown) which is reciprocated, as illustrated by arrow 52 in FIG. 8 of the drawings. Each MEMS chip 20, when it is desired to remove it, is exposed to UV light as indicated by arrows 54 through a mask 56. This cures the adhesive of the tape 40 locally in a region beneath one particular MEMS chip 20 at a time to enable that MEMS chip 20 to be removed from the tape 38. The MEMS chip 20 is removed from the tape 38 by means of a transporting means including a vacuum pickup 58.

Hence, it is an advantage of the invention, that a method of fabrication is provided which facilitates the performing of various operations to fabricate the individual MEMS chip 20 and which facilitates removal of the MEMS chips 20 for packaging. It will be appreciated that devices of the kind in question are measured in micron dimensions. Accordingly, the MEMS elements 18 on such devices are extremely fragile. The provision of the nozzle guard layer 10 and the use of the UV curable tape 38 facilitates that the MEMS elements 18 are not touched by solids or liquids after they are released by the release etch.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 

1. A method of fabricating microelectromechanical systems devices, the method comprising the steps of: forming a plurality of microelectromechanical systems elements on a first surface of a silicon substrate; applying a guard layer to the first surface of the silicon substrate, the guard layer defining a plurality of recesses and respective microelectromechanical systems elements are received within respective recesses; segmenting the silicon substrate into discrete parts, each discrete part including at least one microelectromechanical systems element; bonding an adhesive layer to a second surface of the silicon substrate, the second surface being opposite said first surface; segmenting the guard layer corresponding to the discrete parts of the silicon substrate thereby forming individual microelectromechanical systems devices; and selectively exposing the adhesive layer to a light source allowing removal of individual microelectromechanical systems devices.
 2. A method as claimed in claim 1, wherein said light source is an ultraviolet light source.
 3. A method as claimed in claim 1, wherein said light source exposes said adhesive layer through a mask.
 4. A method as claimed in claim 1, further comprising the step of applying a handling layer to the adhesive layer so that the adhesive layer is located between the handling layer and the substrate, said handling layer being at least partially transparent.
 5. A method as claimed in claim 1, wherein said microelectromechanical systems devices are printheads and said microelectromechanical systems elements are ink ejection nozzles, said method comprising the further step of etching a plurality of ink supply channels in the second surface of the silicon substrate prior to bonding the adhesive layer to the second surface.
 6. A method as claimed in claim 5, comprising the further step of etching a plurality of ink ejection channels in the guard layer so that each ink ejection channel is in register with respective ink ejection nozzles. 